The invention relates generally to touch panel display systems, and more particularly, to sealing light beam touch panel display systems against electromagnetic energy interference.
Patents disclosing such touch panel display systems include U.S. Pat. No. 3,764,813 to Clement et al., granted Oct. 9, 1973; U.S. Pat. No. 3,775,560 to Ebeling et al., granted Nov. 27, 1973; and U.S. Pat. No. 4,198,623 to Misek et al., granted Apr. 15, 1980. In systems such as these where light beam sources direct beams of light across the face of a display toward light beam detectors located on the other side of the display, electromagnetic energy may escape from the display unit and allow its detection and it may also interfere with sensitive electronic equipment in the immediate area. Also, external electromagnetic energy may enter the display unit and interfere with its operation. Prior electromagnetic energy shielding arrangements for touch panel display units have been complex, bulky, and have not been sufficiently integrated with the display unit. These prior arrangements have, in some cases, made maintenance of the display unit more difficult and have typically not been of the type which also enhance display operations.
Various internal touch panel circuits as well as various display circuits generate signals which may radiate from the display unit. Where square wave signals are used inside the display unit, harmonics of relatively high frequency may escape. Where the touch panel display unit is to be used in an environment requiring the control of compromising emanations, suppressing the radiation of such signals may be required in order to avoid detection. In the case where the display unit is located near other equipment which radiates electromagnetic energy, such as a radar system, exposure of the display unit circuits to that energy may cause faults, processing errors or have other detrimental effects on display unit operation. As used herein, electromagnetic energy interference refers to signals which are of lower frequency than that of the touch panel light beams.
Prior touch panel light beam systems are also susceptible to extraneous light striking the light beam detectors. Such light lowers the signal to noise ratio of the light beam system and, if intense enough, may disable the system since the detector will be biased by the extraneous light and will not sense an interruption in the light beam. An effect such as this occurs in some prior light beam systems near the edge or border of the display. In that area, the light beam may be reflected by the raised border of the display and strike the detector at an angle acute to the straight line between the light beam source and dectector. If the reflection is strong enough, the detector will be biased by such reflection and will not sense an interruption of the main beam in certain places. A prior technique for defeating this border reflection is installing a protruding opaque object or "reflection fence" at the border to disrupt reflections. However, this technique does not solve the problem of lowered signal to noise ratio due to extraneous light.
Accordingly, it is an object of the invention to provide an electromagnetic energy interference seal which impedes the propagation of electromagnetic energy interference into and out of a touch panel display unit.
It is also an object of the invention to provide an electromagnetic energy interference sealing arrangement for use in a touch panel display system which reduces the amount of extraneous and ambient light reaching the light beam detectors thereby resulting in an improved signal to noise ratio in the touch panel area.
It is also an object of the invention to provide an electromagnetic energy interference sealing arrangement for use in a touch panel display system having improved efficiency and improved reliability over prior touch panel display system seal arrangements.